1. Field of the Invention
The present invention relates to a process for the co-production of methanol and ammonia from a hydrocarbon feed without venting to the atmosphere carbon dioxide captured from the methanol and ammonia synthesis gas and without using expensive water gas shift and carbon dioxide removal steps. More particularly the invention is concerned with a sequential and once-through (single pass) process for the co-production of methanol and ammonia without water gas shift and carbon dioxide removal and without air separation unit used in the reforming section of the plant.
2. Description of the Related Art
Current processes for co-production of methanol and ammonia involve generally parallel processes in which a common reforming section is used to generate a synthesis gas which is split in separate parallel streams, one of which is used for methanol synthesis and the other for ammonia synthesis. The co-production of methanol and ammonia can also be conducted sequentially or in series, where the synthesis gas produced in the reforming section is first converted to methanol and the unreacted gas containing carbon oxides and hydrogen is subsequently used for ammonia synthesis. Water gas shift and/or carbon dioxide removal steps of the synthesis gas stream are required, thus involving the release of CO2 to the atmosphere and the investment in highly expensive and complicated units for conducting the shift conversion and carbon dioxide removal.
US-A-2007/0299144 discloses in one embodiment a process in which methanol and ammonia are produced in parallel and independently from a common synthesis gas stream and without production of urea. Since urea is not produced there is no need to divert carbon dioxide for urea synthesis. The carbon monoxide in the synthesis gas stream used for ammonia synthesis is converted to carbon dioxide and the reforming is conducted in an oxygen-blown reactor with the oxygen being provided from an Air Separation Unit.
U.S. Pat. No. 6,106,793 describes a process in which methanol and ammonia are produced in parallel and independently. The gas produced in the secondary reforming section is cooled by indirect heat exchange with a gas containing methane and steam in a second primary reforming section to produce an ammonia synthesis gas. The heated gas reacts to produce a methanol synthesis gas comprising CO, CO2 and H2.
EP-A-0,553,631 discloses a process for the production of methanol followed by the production of ammonia. Prior to conducting the ammonia synthesis, unreacted methanol synthesis gas is passed to at CO2-removal step and a nitrogen-wash. An Air Separation Unit provides for the nitrogen in the N2-wash and oxygen for the oxygen-blown secondary reformer upstream the methanol synthesis section.
JP-A-2000063115 describes a process for the co-production of methanol and ammonia. In the reforming section the secondary reformer is air-blown and carbon dioxide is removed from the synthesis gas in order to adjust the syngas composition. There is no need of a shift reactor for converting CO into CO2. The synthesis gas is used for production of methanol in a process which uses recirculation of product stream. Process purged gas from the methanol section is subjected to methanation and then used for ammonia production.